Experimental and Modeling Studies of the Degradation of Estrogen Hormones in Aqueous TiO₂ Suspensions under Simulated Solar Radiation

Abstract

The efficiency of TiO 2 photocatalysis to degrade three estrogen hormones, that is, 17α-ethynylestradiol (EE2), estrone (E1), and 17β-estradiol (E2), in environmentally relevant samples was investigated. Radiation at a photon flux of 1.7 × 10 −7 einstein/s was provided by a solar simulator and experiments were conducted at various TiO 2 loadings (25−1500 mg/L), estrogen concentrations (85−300 μg/L in individual solutions and 400 μg/L in mixture), and water matrices (ultrapure water, drinking water, and secondary treated wastewater). Changes in estrogen concentration were followed by high performance liquid chromatography and estrogenicity by the yeast estrogen screening assay. Aeroxide P25, a commercially available mixture of 75:25 anatase/rutile, was considerably more active than carbon-doped and undoped anatase titania, with degradation increasing with increasing catalyst loading and treatment time. The organic and inorganic constituents typically found in wastewater and drinking water impeded degradation presumably due to the scavenging of oxidizing species. For example, the time needed for complete 100 μg/L EE2 degradation in pure water was an order of magnitude lower than that in wastewater. The three estrogens exhibited comparable reactivity, with E1 being slightly more reactive than the rest. Degradation in multicomponent mixtures was slower than in individual solutions, thus implying estrogen competition for oxidizing species. Although the mixture of three in wastewater could be degraded fully after 120 min, overall estrogenicity was reduced by just about 30%, highlighting the role of the complex water matrix. Several oxidation products of EE2 were identified by means of LC−MS/MS and a reaction network for the photocatalytic degradation of EE2 is suggested. An artificial neural network comprising five input variables (reaction time, TiO 2 and EE2 concentration, organic content, and conductivity of the water matrix), eight neurons and an output variable (conversion) was optimized, tested, and validated for EE2 degradation. The network, based on tangent sigmoid and linear transfer functions for the hidden and input/output layers, respectively, and the Levenberg−Marquardt back-propagation training algorithm, can successfully predict EE2 degradation.

Simultaneous removal of estrogens and pathogens from secondary treated wastewater by solar photocatalytic treatment

“…This behaviour has been observed several times from our group in the degradation of organic compounds by heterogeneous photocatalysis (Frontistis et al, 2012a, Frontistis et al, 2012b and photocatalytic disinfection (Chatzisymeon et al, 2011).…”

“…Detection was achieved through a fluorescence detector (Waters 474 Scanning Fluorescence detector), in which the excitation wavelength was 280 nm and the emission wavelength was 305 nm. Under these conditions, the retention time was 5.1 min, the limit of detection (LOD) was 0.63 μg l -1 and the limit of quantitation (LOQ) was 2.11 μg l -1 (Frontistis et al, 2012a).…”

“…This can be explained taking into account that (i) the oxidizing agents are competitively consumed in reactions involving the natural organic matter present in treated WW but not in pure water and constitutes most of the matrix's total organic content; (ii) hydroxyl radicals may be scavenged by bicarbonates, chlorides and sulfates present in WW to form the respective radicals, whose oxidation potential is lower than that of hydroxyl radicals (Frontistis et al, 2012a) …”

Hydrothermal synthesis of montmorillonite/hydrochar nanocomposites and application for 17β-estradiol and 17α-ethynylestradiol removal

“…[3][4][5] There are direct or indirect effects on the normal hormone activities via receptor-mediated processes mimicking endogenous hormones.…”

Characterization of BiOX compounds as photocatalysts for the degradation of pharmaceuticals in water

“…There is a need to effectively degrade them. TiO 2 has been studied as a means of degrading EE2 but a prolonged exposure (over 1 h) and/or use of a high energy (254 nm) UV source were required [4,[22][23][24]. The kinetic mechanisms for the photocatalysis of the estrogens will provide essential knowledge on how BiOX catalysts interact with estrogens and related compounds.…”